Evaluation of Unsupported Structural Exciters

Wright Laboratory is evaluating a new vibration calibration technique that allows one person to perform end-to-end calibrations of a structural dynamics measurement system including mounted transducers, signal conditioning and recorder. This new technique uses an unsupported structural exciter(USE). This technique stimulates structural measurement transducers, inside of structures, with a measurable acceleration level. If a transducer is mounted on a test structure, it is difficult to stimulate the transducer with a known physical input. A person must hold the exciter or attach a conventional vibration shaker to a structure. Two persons are required to calibrate, one at the transducer holding the exciter and one at the measurement system. Now one person can calibrate. Laboratory engineers conducted an experiment to evaluate a commercial off-the-shelf vibration paging system consisting of a master control unit and 8 individual exciters(pagers) to excite accelerometers mounted on structures. An accelerometer on the front of the structure measured the vibration input. This paper discusses the instrumentation and a completely randomized block design experiment consisting of three 2-level experimental factors: structural material, structural thickness and excitation mode. A blocking factor was each of the 8 different exciters(pagers) serial numbers. For each of the 64 combinations, a technician used a spectrum analyzer to record and compute the output amplitude, fundamental frequency and transfer function between the two accelerometers. This paper presents results from the experiments and describes the new technique.